Beware, I'm just guessing here. I assume the "boom logo" is the boomerang, shown in the illustration you linked to in magenta, rather than blue and navy, so I think the illustration does not correspond to the text. Also, the logo is clearly sewn onto the swim suit in the illustration, not spliced on. So this may be all wrong...
But ... plowing blithely ahead ... first, regarding the English term: "Splicing is the technique used in the cutting room during the process of spreading. It basically incorporates cutting the fabric across its width to overlap layers in between the ends of the lay." https://medium.com/@stitchdiary/are-you-wasti...
Now I'm always skating on thin ice when I suggest a German translation of an English word (and I'm often wrong!), but it appears that to splice can be translated as Spleißen also when it comes to fabrics.
And the term Spleißen appears to used in German for the corresponding process: e.g. Ultraschallschneiden schneidet und versiegelt das Material gleichzeitig, wodurch ein Ausreißen oder Ausfransen verhindert wird. Es entsteht eine saubere, konische, wulstfreie Kante. Typische Anwendungen sind das Schneiden von Rollenware auf Maß, das Spleißen von auf Länge geschnittenen Rollen. https://www.dukane.com/de/kunststoffschweisma...
So -- once more, I'm just guessing, and this may be completely wrong -- please confirm with GNS -- perhaps gebogener Spleiß, or perhaps simply runder Spleiß. (But if the illustration given in the original post is of the referenced swimsuit with the Boom logo, then my speculation is surely wrong.)
